“They have one week to leave” the U.K., May said in a statement at the House of Commons. 

May said Russia was “culpable” for the incident that took place in Salisbury, England on March 4. 

Russia missed a midnight Tuesday deadline by London to explain how a certain type of military-grade nerve agent was used in the attack.

Sergei Skripal, 66, and his daughter Yulia, 33, were admitted to a hospital after being found unconscious in the southern English city of Salisbury. 

“Mr. Skripal and his daughter were poisoned with a military-grade nerve agent of a type developed by Russia,” specifically from the Novichok group, May said on Monday. 

The incident has drawn comparisons to the 2006 death of former KGB agent Alexander Litvinenko after drinking radioactive tea. Former KGB bodyguards identified as suspects in the murder denied any involvement.  

Skripal was granted refuge in the UK following a 2010 spy exchange between the U.S. and Russia. Before the exchange, he was serving 13 years in prison for leaking information to British intelligence.